Yeah I'm getting the Pro 250ohm. Also, what qualifies as a decent source? I use a TASCAM US-100 audio interface right now if that fits the bill. Also, that LittleDot Mk2 is nearing the price I'm paying for the headphones currently. Are there any more frugal options available / will most tube amps do the job well? From what I've read on Head-Fi my understanding is that the 880s are picky when it comes to amps.
A decent source is any good DAC to be honest. I don't have experience with your source but I'm assuming It would get the job done.
Another option would be the Bravo Audio ocean tube amp, I've heard a lot of great things about this little amp.